BROADBAND TECHNOLOGY
Whenever you hear the term “broadband,” it generally refers to a high-speed interconnection or Internet access. Most broadband systems provide data rates from roughly 1 Mbps or less to well over 10 Mbps, depending on the level of service purchased. Such broadband services are usually provided by cable TV companies or telephone carriers. Other smaller organizations also offer various other types of Internet connectivity.
Cable TV Connectivity
Most cable TV companies offer high-speed Internet connectivity services. What they do is allocate one or more of the 6-MHz wide channels on the cable to this service. (See Chapter 11 on TV.) By using QPSK, 16-QAM, or 64-QAM, a wide range of customers can be offered multiple levels of Internet connectivity service. The customer gets a cable TV modem that connects to the cable along with the TV set. This modem provides the connectivity to a computer via Ethernet. A Wi-Fi access point is often connected to the cable modem to provide wireless connections to the Internet for PCs and laptops.
Digital Subscriber Lines
Digital subscriber lines (DSLs) are high-speed Internet connections that use standard telephone lines. DSL uses the standard twisted-pair telephone lines that come into every home for normal telephone service. These lines, because they were developed only for voice signals, are restricted in bandwidth and data rate. However, special techniques have been developed to allow very high-speed data transmissions on them. DSLs, also referred to as asymmetric digital subscriber lines (ADSL), use a variation of OFDM called discrete multitone (DMT). What it does is divide the restricted bandwidth of the twisted- pair cable into multiple OFDM channels, each 4 kHz wide. Then the data to be transmitted is divided into parallel paths and modulated using some form of QAM. All of this is handled by a DSL modem connected to subscribers’ computers and the home telephone lines.
The speed potential of an ADSL line depends on how far away the sub- scriber is from the central office. The greater the distance, the lower the data rate. For even the longest runs from 12,000 to 18,000 feet, data rates of up to about 2 Mbps are possible.
Newer versions of ADSL have also been developed to permit data rates of up to about 12 Mbps at a range of 8000 feet and 20 Mbps at a range of about 4000 feet. A newer version referred to as video DSL or VDSL extends the bandwidth further and uses higher-level versions of QAM to get data rates of up to 52 Mbps.
Wireless Broadband
Wireless broadband services are only beginning to become available. A relatively new WiMAX wireless network known as XOHM is offered by Clearwire, a spinoff of Sprint Nextel. It provides fixed wireless data services with data rates in the 1- to 3-Mbps range. WiMAX modems are connected to computers that access nearby base stations within several miles of one another.
The beauty of wireless broadband is that no cables or other hard connectivity is required. These are easy to set up, although at microwave frequencies, range is a problem as are multipath problems with buildings, trees, and other obstructions. However, with high enough antennas and sufficient power, wire- less broadband has proved to be practical. It is growing rapidly, particularly in those areas where DSL and cable TV services are not currently available. This is particularly true in rural areas and in some small towns and communities.
Don’t forget that wireless Internet connectivity can also be achieved by using the regular cell phone networks. You can purchase a data modem that plugs into your laptop USB connector on a PC. This modem connects you just as it would a cell phone to your cellular network. From there you can use the 3G data service to connect to the Internet, access email, or perform other networking operations.